Use algebra to Solve the proportions?

Question

(fractions)
y/4 = 42/28
b/45 = 8/9
39/54 = d/18
3/7 = z/63

Answer 1

1) y/4 = 42/28
28y = 42*4
y = 168 : 28
y = 6
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b/45 = 8/9
9b = 45 * 8
b = 40
><
39/54 = d/18
54d = 18 * 39
d = 13
><
3/7 = z/63
7z = 63 * 3
z = 27
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Answer 2

Just use cross multiplication:

y/4 = 42/28 , which can also be represented by:

y * 28 = 4 * 42
y * 28 = 168, simplified further:

y = 168/28
y = 6

You can remember it like this:

a/b = c/d

Which can be rewritten as:

a * d = b * c

And to find a missing variable, divide the side where all of the information is given by the given number on the side with the missing variable, so if you're looking for "d", it would look like this:

(b * c) / a = d

And it can be rewritten many ways to find every variable in the problem.

So for the rest of your problems it should look something like this:

2.) b/45 = 8/9

b * 9 = 45 * 8
b * 9 = 360
b = 360 / 9
b = 40

3.) 39/54 = d/18

39 * 18 = 54 * d
702 = 54 * d
702/ 54 = d
d = 13

4.) 3/7 = z/63

3 * 63 = 7 * z
189 = 7 * z
189 / 7 = z
z = 27

Answer 3

y/4=42/28
y=4(42/28)
y=6
then fraction is 6/4=42/28

b/45=8/9
use the same step above
b=45(8/9)
b=40
then answer is 40/45=8/9

39/54=d/18
same procedure
(39/54)18 = d
13=d, or you can write it d = 13
you got 39/54=13/18

3/7 = z/63
(3/7)63=z
you got z=27
ans. 3/7=27/63

Answer 4

cross multiply

y/4=42/28= 28y=168 y=6
b/45=8/9=9b=360 b=40
39/54=d/18= 54d=702 d=13
3/7=z/63= 7z=189 z=27

Answer 5

y/4=42/28 (convert y/4 to have the same denominator as the 28)
7y/28 = 42/28 (multiply by 28)
7y=42 (divide by 7)
y=6

b/45=8/9 (same as above)
b/45=40/45
b=40

39/54=d/18
39/54=3d/54
39=3d
13=d

3/7=z/63
27/63=z/63
27=z